New discovery of a koala the size of a house cat could bridge a 30-million-year gap in the fossil record: study

Researchers have unearthed fossils that they say could bridge a 30-million year gap in the evolution of the koala, one of Australia’s most iconic creatures.

Unlike the modern day koala, which takes a bit of muscle to hold in your arms, this newly discovered relative of the koala would’ve been much smaller, around the size of a domestic house cat, according to a recent study published in the peer-reviewed journal Scientific Reports.

It weighed roughly 2.5 kilograms, said Arthur Crichton, study lead and PhD student from Flinders University who discovered fossil teeth of the new species at the Pwerte Marnte Marnte fossil site in Australia’s Northern Territory. The teeth are believed to be around 25 million years old.

Named Lumakoala blackae, this small animal “probably ate mostly soft leaves, but wouldn’t have turned down an insect given the chance,” Crichton said in a press release Thursday.

“Our computer analysis of its evolutionary relationships indicates that Lumakoala is a member of the koala family (Phascolarctidae) or a close relative, but it also resembles several much older fossil marsupials called Thylacotinga and Chulpasia from the 55 million-year-old Tingamarra site in northeastern Australia.”

The Pwerte Marnte Marnte fossil site is thought to be the site containing the oldest terrestrial mammals from the Oligocene (around 33.7 million years ago to 23.8 million years ago), which can be found in Australia.

The discovery of Lumakoala blackae comes from field samples collected from the site in 2014 and 2020 and analyzed by Crichton. Although Pwerte Marnte Marnte contains a wealth of fossils, it’s difficult to remove them from the limestone. These fossils were processed from 2020 to 2022 at the Flinders University Palaeontology Lab using acid, rock saws and other mechanical tools to painstakingly release the fossils from the stone.

The field samples also contained fossils from two other early koala relatives, Madakoala and Nimiokoala, which are also described in the study.

The similarities between Lumakoala blackae’s molars and those of older marsupials found in the Tingamarra site suggest that Lumakoala blackae could be one of the intermediary stages of evolution between those marsupials and the modern day koala.

Comparison of upper molar morphology between Chulpasia jimthorselli, Lumakoala blackae and the modern koala. (A. Crichton / Flinders University)

“These Tingamarran marsupials are less mysterious than we thought, and now appear to be ancient relatives of younger, more familiar groups like koalas,” Robin Beck, associate professor from England’s University of Salford and co-author of the paper, said in the press release.

“It shows how finding new fossils like Lumakoala, even if only a few teeth, can revolutionise our understanding of the history of life on Earth.”

It’s an exciting link in an evolutionary chain that has long been shrouded in mystery.

Australia is home to many unique animals not found anywhere else in the world, including an incredibly diverse range of marsupials.

Diprotodontia is the largest order of marsupials, including kangaroos, wallabies, possums, koalas, wombats and many others, totalling around 155 species.

“This group (Diprotodontia)is extremely diverse today, but nothing is known about the first half of their evolution due to a long gap in the fossil record,” Crichton said in the release.

Molecular analysis suggests that Diprotondontia diverged from Agreodontia — an umbrella order of marsupials which includes species that later evolved into modern-day bandicoots, Tasmanian devils and numbats, among others — sometime between the late Cretaceous period (from roughly 100.5 million years ago to 66 million years ago) and the earliest middle Eocene (roughly 47.8 million years ago).

This means they would’ve diverged before Australia had completely finished separating from Antarctica, which only happened 30 million years ago. Australia and Antarctica were the last remaining pieces of the supercontinent Gondwana to separate from one another.

After separation, what followed was a long period of isolation for Australia, which allowed for the increasingly diverse evolution of marsupials and other species.

However, there’s a lack of marsupial fossils from prior to the late Oliocene, making it hard to follow the path of evolution between much older fossils and newer ones. The key similarities found between Lumakoala’s molars and two 55-million-year-old species potentially offer a way across that gap.

Thylacotinga and Chulpasia are small marsupials whose familial relationships have long been speculated to lie in South America, as it used to be part of Gondwana. Fossils similar to Chulpasia have also been found in Peru.

“In the past, it was suggested the enigmatic Thylacotinga and Chulpasia may have been closely related to marsupials from South America,” Crichton said. “However, the discovery of Lumakoala suggests that Thylacotinga and Chulpasia could actually be early relatives of Australian herbivorous marsupials such as koalas, wombats, kangaroos and possums.

“If our hypothesis is correct, it would extend the Diprotodontian fossil record back by 30 million years.”

The study raises the question of whether the koala’s roots can be traced back to South American and Antarctica. This discovery is also the first time that an ancient relative of the koala has been found in Australia’s Northern Territory.

Although there is only one modern species of koala, there used to be many, with at least seven having been identified as active in the late Oligocene.